Many of the effects of TSH appear to be mediated through cyclic AMP. The regulatory role of cyclic AMP dependent protein kinase in this chain of events will be studied. Particular attention will be paid to the subcellular distribution of cyclic AMP dependent protein kinase activity and phosphoprotein phosphatase activity. In addition, the regulation of cyclic AMP dependent protein kinase activity by various stimulators including TSH, prostaglandins, and adrenergic agents will be studied.